REACTIVE OXYGEN SPECIES (ROS) ARE BOON OR BANE

REACTIVE OXYGEN SPECIES (ROS) ARE BOON OR BANE

Seema Tripathy ^* and Prafulla Kumar Mohanty

Post Graduate Department of Zoology, Utkal University, Vani Vihar, Bhubaneswar - 751 004, Odisha, India.

ABSTRACT: Reactive oxygen species (ROS) are inevitable by-products of cellular respiration. These are highly reactive chemical species derived from molecular oxygen (O₂). These include the superoxide (O₂−) and hydroxyl (HO−) free radicals as well as non-radical molecules such as hydrogen peroxide (H₂O₂). These act as both toxic and beneficial compounds, since they can be either harmful or helpful to the body. Redox regulation or controlled ROS generation is the net effect of a subtle balance between ROS generation and neutralization or utilization by cellular antioxidant systems. The most deleterious effect of ROS is “oxidative stress”. Oxidative stress plays a major part in the development of chronic and degenerative ailments such as cancer, arthritis, aging, autoimmune disorders, cardiovascular and neurodegenerative diseases. Several mechanism exists to counteract oxidative stress. This review provides a detailed overview of the influence of ROS on human pathophysiology and novel therapeutic strategies followed to treat ROS mediated diseases or disorders.

INTRODUCTION: Oxygen (O₂) is a crucial element involved to carry out the metabolic reaction like synthesis and degradation of metabolites in aerobic organisms. According to Lavoisier, O₂ plays dual role in living processes by acting as a sustainer and a destroyer. Reactive oxygen species (ROS) are oxygen-derived small molecules. Most ROS that have been described in living organisms are O₂ ions, peroxides and several non-radical oxidizing agents ¹. These include the superoxide anion (O₂^-), hydrogen peroxide (H₂O₂), hydroxyl ion (OH^-), and nitric oxide (NO).

ROS are often termed free radicals; this does not apply to H₂O₂ and ONOO^- which are non-radical ROS. These react readily with a variety of chemical structures such as proteins, lipids, sugars, and nucleic acids. Is the generation of ROS really a bane for human beings?

It is demonstrated that excess generation of ROS creates a phenomenon called oxidative stress, a deleterious process that can seriously alter the cell membranes and other structures such as proteins, lipids, lipoproteins and deoxyribonucleic acid (DNA). Oxidative stress mediates several diseases including cancer, atherosclerosis, malaria, chronic fatigue syndrome and rheumatoid arthritis and neurodegenerative diseases such as Parkinson’s disease, Alzheimer’s disease, Huntington’s disease, acquired immune deficiency syndrome (AIDS) and aging ².

This review describes the mechanisms of formation and catabolism of ROS, their concerned role in inducing cytopathologic conditions, the importance of antioxidative defense system in ameliorating the toxicity of ROS and novel therapeutic opportunities provided by antioxidants, plant based products, drugs and stem cell therapies to treat the pathologic conditions induced by ROS.

Nature of reactive oxygen species (ROS): O₂ contains two unpaired electrons and can, therefore, undergo reduction, yielding several oxygen metabolites (Fig. 1).

FIG. 1: ELECTRONIC CONFIGURATION OF OXYGEN

Its oxidation number ranges from 0 (O₂) to -2 (H₂O). So, it can execute nucleophilic addition, nucleophilic substitution and chain reaction. ROS react quickly with other compounds and try to capture the required electron to gain stability which itself explains their normal biological activities and damaging effects on cells. During cellular respiration some amount of O₂ escapes from this ordered process and is released as ROS. Mitochondria are not only responsible for production of ROS but at the same time they are also target of ROS to generate diseases ^{3, 4}. Then why does generation of ROS still remain mitochondrial paradigm? The different factors involved in the intricate generation of endogenous and exogenous ROS by different cell organelles and environment (Fig. 2). Once an ROS is initiated, a chain reaction starts with a cascade and finally results in the disruption of a living cell. The ROS are generated via different types of physiologic reactions (Table 1).

FIG. 2: GENERATION OF ROS BY DIFFERENT INTRINSIC AND EXTRINSIC FACTORS

TABLE 1: GENERATION OF DIFFERENT TYPE OF ROS

Exogenous ROS generated from air and water pollution, cigarette smoke, alcohol, heavy or transition metals (Cd, Hg, Pb, Fe, As), certain synthetic drugs such as antibiotics (cyclosporine, tacrolimus, gentamycin, bleomycin). Non-steroidal-anti-inflammatory drugs (NSAIDs) are used widely in the treatment of pain, fever, inflammation, rheumatic and cardiovascular disease but chronic administration of those drugs leads the generation of free radicals which may result gastric erosions, duodenal ulceration and severe complications such as gastrointestinal hemorrhage and perforation. The exogenous compounds like industrial solvents, smoked meat, used oil fat and radiation after penetration into the body by different routes are decomposed or metabolized into free radicals ^{2, 5}. Different ROS significantly differ from each other in their properties that include reduction potential, half-life and intracellular concentration (Table 2).

TABLE 2: DIFFERENT PROPERTIES OF SOME TYPICAL ROS

“Good” and “evil” of ROS:  Miscellaneous ROS are double-edged sword, available abundantly in biological system. Their production may be accidental or deliberated. ROS dose in living system is a critical parameter in determining the ultimate cellular response. At low or moderate concentration, ROS are necessary for cell signaling and maturation process of cellular structures, cell homeostasis, maintenance of tissue architecture and functional integrity ⁹.

ROS regulate Ras/Raf/MEK/ERK and Ras/ PI3K/ PTEN/Akt transcription factors pathways. The most active ROS like “superoxide” confer immunity directly by showing the mechanisms of “respiratory burst” or indirectly by stimulating various non-oxidative mechanisms that include pattern recognition receptors, signaling, autophagy, neutrophil extracellular trap formation and T-lymphocyte responses ¹⁰. Several evidences suggest that ROS play important role in implantation of blastocysts, disintegration of the structural elements of the sperm cells, iodination of tyrosine in the thyroxine biosynthesis and secretion of mucus in goblet cells ¹¹.

Immunological functions: ROS act as weapons for the host defense system. Indeed, phagocytes (neutrophils, macrophages, monocytes) release free radicals to destroy invading pathogenic microbes ^{12, 13}. The main enzyme system responsible for ROS production from phagocytic cells is the family of nicotinamide adenine dinucleotide phosphate (NADPH) oxidases (NOXs) which consist of seven members from NOX (1 to 5) and two dual oxidases, Duox1 and Duox2 ¹⁴. These enzymes are responsible for generation of superoxide anion or hydrogen peroxide as primary products and actively exhibit physiological, pathological functions and form confirmative defense against infection ¹⁵. They elicit their defense action by the production of NOX2. NOX2 is responsible for the release of superoxide in the phagocytic vacuole, promotion of bacterial killing and the execution of respiratory burst. Chronic granulomatous disease (CGD) or Quie syndrome is a diverse group of hereditary disease in which certain cells of the immune system are unable to form the reactive O₂ compounds (superoxide radical).

So patients of this disease experience multiple and persistent infection. This leads to the formation of granulomata in many organs ¹⁶. CGD affects about 1 in 2, 00,000 people in the United States, with about 20 new cases diagnosed each year ¹⁷.

Cellular responses to ROS: ROS tightly regulate a variety of proteins involved in cell proliferation and survival. They either trigger the initial process or direct regulation of signaling molecules at “oxidative interface region”. ROS directly interact with key regulatory components of MAP kinases, PI3 kinase, PTEN and protein tyrosine phosphatases signal transduction pathways involved in proliferation and survival. ROS are involved in tissue homeostasis by controlling mitochondrial oxidative stress, apoptosis, and ATM regulated DNA damage response and aging (p66Shc), iron homeostasis through iron–sulfur cluster proteins (IRE–IRP), and antioxidant gene regulation (thioredoxin, peroxiredoxin, Ref-1 and Nrf-2) ¹⁸.

Mobilization of ion transport system: ROS induce modifications in ion transport pathways by the following mechanisms such as oxidation of sulfhydryl groups located on the ion transport proteins, peroxidation of membrane phospholipids and inhibition of membrane-bound regulatory enzymes and modification of the oxidative phosphorylation and ATP levels. These deleterious effects of ROS are due to their interaction with various ion transport proteins underlying the transmembrane signal transduction such as (i)  ion channels [Ca²⁺ channels (include voltage-sensitive L-type Ca²⁺ currents, dihydropyridine receptor voltage sensors, ryanodine receptor Ca²⁺ release channels, and D-myo-inositol 1,4,5-trisphosphate receptor Ca²⁺ release channels), K⁺ channels (activated K⁺ channels, inward and outward K⁺ current and ATP-sensitive K⁺ channels), Na⁺ channels and Cl^- channels)], (ii) ion pumps [sarcoplasmic reticulum and sarcolemma Ca²⁺ pumps, Na⁺-K⁺ ATPase pump, Na⁺ pump, and H⁺-ATPase pump (iii) ion exchangers such as the Na⁺/Ca²⁺ exchanger and Na⁺/H⁺ exchanger and (iv) ion co-transporters [K⁺-Cl^-, Na⁺-K⁺-Cl^- and Pi-Na⁺ co-transporters].

Alteration in the ion transport mechanism may lead to changes in a second messenger system, primarily Ca²⁺ homeostasis. This further augments the abnormal electrical activity, disrupts signal transduction and promotes cellular dysfunction which may become major cause to induce pathological conditions ¹⁹.

Apoptosis: ROS at lower concentration act as signaling molecules. These are responsible for activation of an apoptotic cell signaling cascade by accumulating in the mitochondrial membrane ²⁰. Cell signaling by ROS would not appear to be random, as previously assumed, but they may target at specific metabolic and signal transduction pathways of some cellular components after generation ²¹. ROS lead to intrinsic pathway of apoptosis by permeabilization  of the mitochondrial membrane. H₂O₂ causes the release of cytochrome c from mitochondria into the cytosol and also activate nuclear transcription factors like NF-κB, AP-1 and p53. These phenomena may up-regulate death proteins or produce inhibitors of survival proteins. The intrinsic pathway induced through mitochondrial damage leads to many mitochondrial disorders. H₂O₂ also induces extrinsic pathway of apoptosis by up-regulation of the Fas-FasL system. This activation of Fas ligand via phosphorylation is necessary for subsequent steps of apoptosis leading to cell death by releasing cytochrome c outside the mitochondria ²².

Diseases: ROS cause 38 million deaths per year globally with rising prevalence across the world particularly in developing countries. This may be due to the fact that ROS provoke macromolecular damage within the cells and result many chronic and acute diseases (Fig. 3).

FIG. 3: OXIDATIVE STRESS AFFECTS HUMAN PHYSIOLOGY AT MOLECULAR LEVEL.

Nevertheless, the molecular mechanism by which ROS induce fatal effects on active bio-molecules is not yet fully elucidated. However, the etiology and prognosis of such diseases largely rely on genetic susceptibility of host, environmental factors and personal habits. After entering a cell, virus creates an imbalance in the cell’s ROS system. Do ROS generate inside host regulate lysogenic and lytic cycle of virus? Data represented in Reshi et al. ²³ suggest that patients infected with RNA viruses are under chronic oxidative stress, play a dominant pathogenic role in human immunodeficiency virus (HIV), hepatitis and influenza infection. Here, persistent viral infection is sufficient reason of over production of ROS making the situation more complicated in people suffering from diseases like hepatitis B, hepatitis C and influenza (H1N1).

AIDS: AIDS is characterized by a decrease in the CD4 lymphocytes. AIDS is the end phase of HIV infection. The fluctuation in the ROS concentration induced apoptosis of CD4 cells and dysfunction of other immune system components seem to contribute to the progression of AIDS.  Due to weakening of antioxidant system, the level of glutathione (GSH), cystine, vitamin C and superoxide dismutase (SOD) are decreased and the serum malondialdehyde (MDA) and 4-hydroxynonenal (HNE) levels are elevated in patients infected with HIV-1 ²³. The nuclear transcription factor NF-?B, which is necessary for viral replication, is activated by ROS and combined effects of MA and gp120 disrupt arrangement of tight junction proteins causing irreversible damage to blood brain barrier (BBB). Thus, facilitating the entry of infected monocytes into astrocytes and microglia of central nervous system (CNS) leading to neurodegenerative disorders in case of AIDS patients.

Hepatitis C:  Hepatitis C virus (HCV) infection has become pandemic affecting 3% of total world population. HCV is a positive-stranded RNA virus that causes severe liver diseases, such as cirrhosis and hepatocellular carcinoma. HCV uses an RNA-dependent RNA polymerase to replicate its genome and an internal ribosomal entry site to translate its proteins. HCV infection is characterized by an increase in the concentration of ROS. Choi et al. ²⁴ reported that ROS can rapidly inhibit HCV RNA replication in human hepatoma cells.

The increased ROS level in hepatitis C patients may, therefore, play an important role in the suppression of HCV replication. The HCV polyprotein precursor when cleaved by viral proteases and host cell signal peptidases results in at least three structural (core, E1 and E2) and six nonstructural proteins (NS2, NS3, NS4A, NS4B, NS5A and NS5B). Reports have shown that HCV gene expresses core protein in the host cell that in turn increases the level of ROS through the mediation of calcium signaling. The NS5A protein of HCV causes alterations in Ca²⁺ homeostasis. The release of calcium from the ER results in an increase in ER stress. The released calcium taken up by the mitochondria results in increased ROS production and oxidative stress. ROS are involved in transcriptional activation of a large number of cytokines and growth factors. This continuous production of ROS acts as fuel for the vicious cycle.

Oxidative stress causes hepatic damage and enhances occurrence of non-reparative damage. Consistent viral infection in hepatitis increases ROS level resulting in decrease in cellular concentration of GSH and increase level of oxidized thioredoxin and lipid peroxidation products. HCV core gene expression has been associated with increased ROS, decreased intracellular and/or mitochondrial GSH content ²⁵. Thus, viral induced ROS production further exaggerates the problems to hepatocellular carcinoma and other associated liver disorders like fibrosis and cirrhosis, various metabolic alterations including steatosis and insulin resistance associated with fibrosis progression or iron overload and the development of HCC or non-Hodgkin lymphoma.

Influenza (H1N1): Influenza, a virus-induced lung disease caused by influenza A virus (IAV) leads to substantial mortality and economic loss worldwide with 2, 00 000 annual hospitalization in the US and 5, 00, 000 additional deaths globally per year and this figure reaching million number of death. The excessive production of ROS like superoxide and hydrogen peroxide decreases GSH synthesis that plays a pivotal role for influenza virus replication by allowing the folding and maturation of viral haemagglutinin.

Mitochondrial ROS might be responsible for controlling IAV infection and may be potential sources of ROS generation ²⁶. NADPH oxidase 2 (Nox2), has a prominent role in increasing severity of symptoms of influenza. Thus, it may assume that the use of Nox2 oxidase inhibitors in preparation of antivirals vaccines could suppress influenza.

Fetal growth: Fetal programming occurs when the normal pattern of fetal development is disrupted by an abnormal stimulus or ‘insult’ applied at a critical point in in utero development. The ‘insults’ that alter placental development include hypoxia, oxidative and abnormal maternal nutrient status, to which the placenta may adapt by alterations in transporter expression and activity to maintain fetal growth or by epigenetic regulation of placental gene expression ^{27, 28}. The increasing metabolic activity of placental mitochondria throughout gestation results in increasing oxidative stress in a normal pregnancy. This oxidative stress is exacerbated in pregnancies complicated by pre-eclampsia or diabetes that can be measured by production of ROS or by decreased level of antioxidant enzymes ^{29, 30}.  Thus, produced ROS include superoxide and nitric oxide, both of which can be produced by trophoblast. Trophoblast and placental villous vascular endothelium express NADPH oxidase (NOX) 1 and 5 isoforms, which are probably the major enzymatic sources of superoxide in the placenta. In pregnancies complicated by pre-eclampsia, increased expression of both NOX 1 and 5 are seen ³¹.

Cardiovascular diseases: Chronic kidney diseases (CKD) and cardiovascular diseases (CVD) are unified with oxidative stress. These are further provoked by diabetes, obesity, metabolic syndrome, smoking or genetic predisposition, increasing age and acute injury. The progression of CKD to CVD or vice versa is mediated by events like (i) inflammation and the release of pro-inflammatory cytokines such as tumor necrosis factor-α (TNFα), interleukin-1β (IL-1β) and IL-8 from activated lymphocytes, (ii) endothelial dysfunction due to increased retention of uremic toxins and decreased L-arginine synthesis which causes alterations in nitric oxide (NO) signalling - dyslipidaemia and associated pro-oxidative/inflammatory state lead to increased oxidised-low density lipoproteins (ox-LDL), a major component in the pathogenesis of atherosclerosis and (iii) redox perturbations ³². All these factors create imbalance between the production ROS or reactive nitrogen species (RNS) and endogenous antioxidants. This leads to mitochondrial dysfunction and alterations in redox sensitive pathways such as Nrf2/keap1/ARB.

Cancer: The role of ROS in cancer is controversial as it promotes as well as inhibits cell proliferation. ROS make rapid and transient second messenger molecules for signal transduction and signal amplification. Specifically, T cells generate hydrogen peroxide and/or superoxide. In fact, certain cancer drugs aim in increasing the free radical amount in body. Several anticancer agents, collectively termed redox therapeutics act by increasing intracellular level of ROS. It was observed that the combination of doxorubicin and mitomycin C are supra-additive tumor cell killing chemicals in vitro in both murine and human breast cancer cells and in vivo against murine breast cancer cells ³³.

Recently, Singer et al. ³⁴ have demonstrated that glioblastoma, a sub-population of tumor cells with stem cell-like properties, glioma stem cells (GSCs), is specifically endowed to resist or adapt to the standard therapies, leading to therapeutic resistance. This is the most common cause of tumor recurrence, which is ultimately fatal in 90% of the patients 5 years after initial diagnosis has been suppressed by redox modulator cannabidiol (CBD).  CBD induces a robust increase in ROS, which inhibit cell survival. The regulation of ROS generation may provide a novel strategy to control cancer progression.

Aging: Aging is an extremely complex process that affects most of the biological functions of an organism, generally culminating in disease and death due to the accumulated actions of different types of stresses. Among these stresses, oxidative reactions accelerate aging of an organism that decline physiological functions mimicked aging process by accumulation of damaged products. Although the statement “aging is a disease” remains at paradox, it is perhaps due to involvement of mitochondrial ROS during the process of aging.

mtDNA is constantly exposed to ROS generated by the mitochondrial electron transport chain and mutations may accumulate exponentially with age. The simultaneous increase in lipid peroxidation and oxidation of mitochondrial proteins adds to the oxidative stress effects, initiating the vicious cycle of molecular degeneration ³⁵. This putative vicious cycle can operate at different rates in various tissues, leading to differential accumulation of oxidative damage, which could explain the differences in functional impairment and deterioration of different tissues in the aging process. A considerable damage happens to mtDNA that progresses with age. Among them, the most significant is the 10-fold increase in an oxidative damage marker (8-hydroxy-2-deoxyguanosine) in mtDNA versus nuclear DNA (nDNA) from human brain ³⁶. A study of aging in rhesus monkeys by Bowling et al ³⁷ has revealed the fact that there is significant decrease in the activities of complex I and IV, as well as in mitochondrial ATP generation with increasing age. Several mtDNA point mutations also increase with normal aging ³⁸.  But are ROS-mediated damages the sole cause of such point mutations?

Oxidative stress impacts deleterious effect on organs and causes organ specific diseases (Fig. 4). ROS play a key role attributing to pathology of diabetes, cardiovascular diseases, and neurological diseases (Table 3). A recent review by Kiranmayi ³⁹ may be referred to detailed understanding of the effect of ROS on human health.

FIG. 4: DELETERIOUS EFFECTS OF OXIDATIVE STRESS ON VARIOUS ORGANS

TABLE 3: SOME OF THE ROS MEDIATED MAJOR DISEASES

Detection of ROS: Due to high reactive nature, it is very difficult to measure ROS directly in biological systems. So, now-a-days fluorescence probes are being used to detect individual ROS. Electron spin resonance Fluorescence probes are currently being used to provide information about the activity and exact location of free radical reactions where it is takes place. That can provide information about the activity and location of free radical reactions.  Considering the technical aspects and cost, the downstream products such as oxidative products or enzyme levels are important parameters for estimation of ROS. Spectrophotometry and chemiluminescence are widely used methods for detection of ROS indirectly. Products like 8-hydroxy-deoxy guanosine (8-OHdG), 8-hydroxy-adenine and 7-methyl-8-hydroxy-guanine resulting from DNA damage by free radicals can be detected in urine.  Lipid peroxidation is an important event mediated in many diseases like atherosclerosis, inflammatory bowel disease (IBD), retinopathy of prematurity (ROP), borderline personality disorder (BPD), asthma, Parkinson's disease, kidney damage, preeclampsia and others. Many assays are available to measure lipid peroxidation, such as MDA by the thiobarbituric acid (TBA) test and diene conjugation. Recently, ferrous oxidation with Xylenol Orange assay coupled with triphenylphosphine has shown to be a reliable marker in determining levels of hydroperoxides (ROOH).  8-epi-prostaglandin-F2α (8-epi-PGF2α) is a marker of oxidative stress derived from oxidation of phospholipids containing arachidonic acid. Oxidative damage to proteins is important as it influences the function of receptors, enzymes and transport proteins.  These can be measured by assay specific for -SH oxidation, carbonyls, aldehyde adducts oxidized tyr, trp, his, met, lys, leu, ileu, val, protein peroxides or hydroxides ⁴⁵.

Mechanisms to nullify ROS: Antioxidants are vital cogs in numerous metabolic reactions and are co-players in redox homeostasis but there are many others cellular molecules of equal importance. The antioxidant defense mechanisms present in animals help to neutralize the generated ROS. The antioxidant defense mechanism act in integrated manner by blocking the initial production of free radicals, scavenging the oxidants, converting the oxidants to less toxic compounds, blocking the secondary production of toxic metabolites or inflammatory mediators, terminating the chain propagation of the secondary oxidants, repairing the molecular injury induced by free radicals or enhancing the endogenous antioxidant defense system of the target ⁴⁶. Humans have evolved highly complex antioxidant systems (enzymic and nonenzymic), which work synergistically, and in combination with each other to protect the cells and organ systems of the body against free radical damage (Fig. 5).

The antioxidants can be endogenous or obtained exogenously as a part of a diet or as dietary supplements. An ideal antioxidant should be readily absorbed and quench free radicals, and chelate redox metals at physiologically relevant levels. It should also work in both aqueous and/or membrane domains and effect gene expression in a positive way. Endogenous antioxidants play a crucial role in maintaining optimal cellular functions and thus, systemic health and well-being. However, the conditions which promote oxidative stress, endogenous antioxidants may not be sufficient and dietary antioxidants may be required to maintain optimal cellular functions ⁴⁷.

Non-enzymatic antioxidants

FIG. 5: MAJOR ANTIOXIDANTS USED TO SCAVENGE ROS.

The antioxidant behavior of polyphenolic compounds, that present in naturally in fruits, vegetables, cereals and beverages show pleiotropic health beneficial effect acting at three different levels (Fig. 6). The antioxidants activate three signaling pathways namely GSH, thioredoxin (TXN) and catalase. TXN is a protein that reduces ROS level which can be regenerated by thioredoxin reductase (TXNR) ⁴⁸. TrxR in conjunction with Trx generates a ubiquitous oxidoreductase system with antioxidant and redox regulatory roles. TrxR-catalyzed regeneration can activate several antioxidant compounds that include ascorbic acid (vitamin C), selenium-containing substances, lipoic acid, and ubiquinone (Q10). GSH synthesis and regeneration of nuclear factor erythroid 2-related factor 2 (NRF2) mainly affects GSH production and NADPH-related responses, forkead box O(FOXO) proteins and the tumor suppressor p53 regulate SODs and catalase ⁴⁸. At the same time different antioxidant pathways are controlled by NRF2. Many signalling pathways that are linked to tumorigenesis can also regulate the metabolism of ROS through direct or indirect mechanisms ⁴⁹.

Treatment of ROS mediated disorders: Despite recent advances in basic and applied biotechnology research and association studies, the optimal therapy for treating ROS mediated disorders are still at a preliminary stage. This may be due to several other agents and factors also associated with ROS mediated diseases. Therefore, direct approach of treating such diseases is rare. Some natural products, synthetic drugs, stem cell therapy and ex vivo gene transfer of stem and progenitor cells are currently used to treat ROS mediated diseases. The synthetic drugs used to treat ROS mediated disorders have many side effects. So, antioxidants therapy is most appealing to patients and clinicians due to low cost and the fact that they can be supplemented along with dietary components. Another important benefit is that these have lower side effects.   Most experts use a combination of vitamins, optimize patients' nutrition and general health and prevent worsening of symptoms during times of illness and physiologic stress. A study by Zeng et al 50 demonstrates that both the anti- and pro-oxidant treatments dramatically influence the survival, apoptosis and ROS production of human umbilical cord derived mesenchymal stem cells (hUCMSCs) through the MAPK-PKC-Nrf2 pathway in vitro. Simultaneously, antioxidant treatment enhances human MSCs anti-stress ability and therapeutic efficacy in an acute liver failure model. It may be due to the fact that antioxidants may activate some anti-stress gene at the cellular level. Plants produce large amount of antioxidants to prevent the oxidative stress, they represent a potential source of new compounds with antioxidant activity. Some of the products derived from plants are currently used in commercially available drugs to treat several neuronal diseases or disorders mediated by ROS (Table 4).

TABLE 4: PLANTS DERIVED PRODUCTS INHIBIT EFFECTS OF ROS GENERATED COMPLICATIONS IN MICE MODEL

Stem cell therapy: ROS accelerate aging and age related complications like osteoarthritis, cardiovascular diseases and muscle fatigue. Stem cell therapy is a form of biological therapy. Stem cells are uncommitted cells present in multicellular organisms throughout life that have the ability to proliferate, perpetuate and differentiate into specialized cell types upon stimulation by appropriate signals. Stem cells can be derived, cultured and expanded in vitro ⁵⁵. Due to several ethical controversies, the application of pluripotent embryonic stem (ES) cells is often prohibited for use in biomedical research in certain countries like India. So multipotent adult stem cells (ASCs) derived from several sources like bone marrow, peripheral blood, adipose tissue, umbilical cord blood (UCB) are widely applied for therapeutic purposes. It has been proposed that endogenous antioxidant level of stem cells could influence their fate after transplantation at injured host sites. For example, endothelial progenitor cells are shown to express high level of antioxidant enzymes and to have increased abilities of DNA repair as compared to more differentiated endothelial cells. Therefore, these are less sensitive to oxidative stress–induced apoptosis ⁵⁶. Recent reports suggest hematopoietic stem cells (HSCs), mesenchymal stem cells (MSCs) and neural stem cells (NSCs) are ideal candidates to treat ROS induced pathological conditions and disorders (Table 5).

TABLE 5: STEM CELLS USED TO TREAT DIFFERENT ROS MEDIATED DISEASES

MSCs are a prototypical adult stem cell actively involved in tissue homeostasis, wound healing and repair processes. Allogeneic transplants of MSCs do not produce any adverse effect which may be due to their inherent immune-tolerance capacity. They release bio-molecules with anti-inflammatory, immunomodulating and anti-fibrogenic properties ⁶². Recent studies have demonstrated that MSCs can be used to treat systemic diseases, local tissue defects or as a vehicle for genes in gene therapy protocols or to generate transplantable tissues and organs in tissue-engineering protocols. Aging is associated with a progressive failing of tissues and organs of the human body leading to a large number of age-related complications ⁶³. In order to treat degenerative or age-related diseases, infusion of stem cells into patients may lessen the complication of disease due to age.

One of the major obstacles to treat neurological disorders involves the delivery of efficacious levels of the drug to the central nervous system (CNS) as they have to cross blood brain barrier (BBB). The BBB regulates the passage of nutrients, ions, and other substances from the blood into the brain. To cross the BBB effectively the molecular weight should be less than 400 dalton (Da) and the substance should show lipophilic and hydrophilic nature and should not be a substrate for an active efflux transporter at the BBB such as p-glycoprotein. Stem cells such as NSCs and MSCs can be used to delivery drugs or RNA to the brain as stem cells can cross the BBB into the brain ⁶⁴. The use of this method to bypass the hurdles of delivering drugs across the BBB is particularly important for diseases with poor prognosis such as glioblastoma multiforme (GBM). Application of

stem cell therapy to deliver drugs to neural tumors is currently in early phase clinical trial stage.

CONCLUSION: ROS are necessary evils. However, production and accumulation of ROS is a very slow process. So, future research must progress in the direction to develop new techniques that would identify the source of ROS, the targets of ROS, specific cell types and organs that may be affected by ROS. So that accumulation of excess amount of ROS can be prevented at appropriate time and proper therapeutic strategies may be followed. Further, research must aim at static treatments for neurological disorders and ROS related other complications like cancer and diabetes. At this juncture, it is a concern for all scientific communities to develop novel microbial strains that can be supplemented with pro-biotic food supplements having ability to scavenge excess ROS, so that ROS related complication could be minimized.

ACKNOWLEDGEMENTS: Authors acknowledge Department of Science and Technology, Government of India for financial support vide reference no SR/WOS-A/LS-13/2016 under Women Scientist Scheme to carry out this work. Authors owe their thanks to Ms Swati Singh, Ms Prerana Mordina and Ms Sony Snigdha Sinku for their critical reading and editing of the manuscript. Thanks are due to the Head, Post-Graduate Department of Zoology, Utkal University, Vani Vihar, Bhubaneswar- 751 004 for providing  the facilities.

CONFLICT OF INTEREST: The authors do not have any conflict of interest.

REFERENCES:

1. Halliwell B: Reactive species and antioxidants. redox biology is a fundamental theme of aerobic life. Plant Physiology 2006; 141: 312–322.
2. Pham-Huy LA, He H and Pham-Huy C. Free radicals, antioxidants in disease and health. International Journal of Biomedical Science 2008; 4:89-96.
3. Wallace DC. Mitochondrial paradigm of metabolic and degenerative diseases, aging, and cancer: a dawn for evolutionary medicine. The Annual Review of Genetics 2005; 39: 359.
4. Marchi S, Giorgi C, Suski JM, Agnoletto C, Bononi A, De Marchi E, Missiroli S, Patergnani S, Poletti F, Rimessi A, Duszynski J, Wieckowski MR and Pinton P: Mitochondria-ROS crosstalk in the control of cell death and aging. Journal of Signal Transduction 2012; 2012: 329635.
5. Sen S, Chakraborty R, Sridhar C, Reddy, YSR and De B: Free radicals, antioxidants, diseases and phytomedicines: current status and future prospect. International Journal of Pharmaceutical Sciences Review and Research 2010; 3:91-100.
6. Kumar S: Free radicals and antioxidants: human and food system. Advances in Applied Science Research 2011; 2:129-135.
7. Johnston RB Jr, Keele BB Jr, Misra HP, Lehmeyer JE, Webb LS, Baehner RL and Rajagopalan KV: The role of superoxide anion generation in phagocytic bactericidal activity. Studies with normal and chronic granulomatous disease leukocytes. Journal of Clinical Investigation  1975; 55:1357-1372.
8. Steinbeck MJ, Khan AU and Karnovsky MJ: Intracellular singlet oxygen generation by phagocytosing in response to particles coated with a chemical trap. Journal Biological Chemistry 1992; 267:13425-13433.
9. Martin KR and Barrett JC: Reactive oxygen species as double-edged swords in cellular processes: low-dose cell signaling versus high-dose toxicity. Human and Experimental Toxicology See comment in PubMed Commons below2002; 21:71-75.
10. Paiva CN and Bozza MT: Are reactive oxygen species always detrimental to pathogens? Antioxidants and Redox Signaling 2014; 20:1000-1037.
11. Hemnani T and Parihar MS: Reactive oxygen species and oxidative DNA damage.  Indian Journal of Physiology and Pharmacology 1998; 42:440-452.
12. Droge W: Free radicals in the physiological control of cell function. Physiological Reviews 2002; 82:47-95.
13. Young I and Woodside J: Antioxidants in health and disease. Journal of Clinical Pathology 2001; 54:176-186.
14. Bedard K and Krause KH: The NOX family of ROS-generating NADPH oxidases: physiology and pathophysiology. Physiological Reviews 2007; 87:245-313.
15. Lassègue B,San Martín A and Griendling KK: Biochemistry, physiology, and pathophysiology of NADPH oxidases in the cardiovascular system. Circulation Research 2012; 110:1364-1390.
16. Heyworth PG, Cross AR and Curnutte JT: Chronic granulomatous disease. Current Opinuon in Immunolpgy 2003; 15: 578-84.
17. Berendes H, Bridges RA and Good RA: A fatal granulomatosus of childhood: the clinical study of a new syndrome. Minnesota Medicine 1957; 40: 309-312.
18. Ray PD, Huang BW and Tsuji Y: Reactive oxygen species (ROS) homeostasis and redox regulation in cellular signaling. Cell Signal 2012; 24:981-990.

19. Kourie JI: Interaction of reactive oxygen species with ion transport mechanisms. The American Journal of Physiology 1998; 275:C1-24.
20. Trachootham D, Lu W, Ogasawara MA, Valle NR.-D and Huang P: Redox Regulation of Cell Survival. Antioxidants and Redox Signaling 2008; 10:1343-1374.
21. Carmody RJ and Cotter TG: Signaling apoptosis: a radical approach. Redox Report 2001; 6:77-90.
22. Kroemer G, Galluzzi L and Brenner C: Mitochondrial membrane permeabilization in cell death. Physiological Reviews: 2007; 87:99-163.
23. Reshi ML, Su YC and Hong JR: RNA viruses: ROS-mediated cell death. International Journal of Cell Biology 2014; 2014:467452.
24. Choi J, Lee KJ, Zheng Y, Yamaga AK, Lai MMC and Ou JH: Reactive oxygen species suppress hepatitis C virus RNA replication in human hepatoma cells. Hepatology 2004; 39: 81-89.
25. Cichoż-Lach H and Michalak A: Oxidative stress as a crucial factor in liver diseases. World Journal of Gastroenterology 2014; 20: 8082-8091.
26. Kim S, Kim MJ, Park do Y, Chung HJ, Kim CH, Yoon JH and Kim HJ: Mitochondrial reactive oxygen species modulate innate immune response to influenza A virus in human nasal epithelium. . Antiviral Research 2015; 119: 78-83.
27. Myatt L: Placental adaptive responses and fetal programming. The Journal of Physiology 2006; 572(Pt 1):25-30.
28. Hracsko Z, Orvos H, Novak Z, Pal A and Varga IS: Evaluation of oxidative stress markers in neonates with intra-uterine growth retardation. Redox Report 2008; 13:11-16.
29. Wang Y, Walsh SW and Kay HH: Placental lipid peroxides and thromboxane are increased and prostacyclin is decreased in women with preeclampsia. American Journal of Obstetrics and Gynecology 1992; 167(4 Pt 1):946-949.
30. Giugliano D, Ceriello A and Paolisso G: Oxidative stress and diabetic vascular complications. Diabetes Care 1996; 19:257-267.
31. Cui XL, Brockman D, Campos B and Myatt L: Expression of NADPH oxidase isoform 1 (Nox1) in human placenta: involvement in preeclampsia. Placenta 2006;  27:422-431.

32. Sugamura K and Keaney JF Jr: Reactive oxygen species in cardiovascular disease. Free Radical Biology & Medicine 2011; 51:978-992.
33. Shuhendler AJ, O'Brien PJ, Rauth AM and Wu XY: On the synergistic effect of doxorubicin and mitomycin C against breast cancer cells. Drug Metabolism and Drug Interaction 2007; 22:201-233.
34. Singer E,Judkins J, Salomonis N, Matlaf L, Soteropoulos P, McAllister S and Soroceanu L: Reactive oxygen species-mediated therapeutic response and resistance in glioblastoma. Cell Death and Disease 2015; (2015) 6:e1601. doi: 10.1038/cddis.2014.566.
35. Yu KR and Kang KS: Aging-related genes in mesenchymal stem cells: a mini-review. Gerontology 2013; 59:557-563.
36. Mecocci P, MacGarvey U, Kaufman AE, Koontz D, Shoffner JM, Wallace DC, Beal MF: Oxidative damage to mitochondrial DNA shows marked age-dependent increases in human brain. Annals of Neurology 1993; 34:609-616.
37. Bowling AC, Mutisya EM, Walker LC, Price DL, Cork LC and Beal MF: Age-dependent impairment of mitochondrial function in primate brain. Journal of Neurochemistry 1993; 60:1964-1967.
38. Kirkinezos IG and Moraes CT: Reactive oxygen species and mitochondrial diseases. Seminars in Cell and Developmental Biology 2001; 12:449-457.
39. Kiranmayi P: Reactive oxygen species: a boon or a bane to human health. International Research Journal of Pharmacy 2014; 5:550-553.
40. Singh PP, Mahadi F, Roy A and Sharma P: Reactive oxygen species, reactive nitrogen species and antioxidants in etiopathogenesis of Diabetes mellitus Type-2. Indian Journal of Clinical Biochemistry 2009; 24:324-342.
41. Wattanapitayakul SK and Bauer JA: Oxidative pathways in cardiovascular disease: roles, mechanisms and therapeutic implications. Pharmacology and Therapeutics 2001; 89:187-206.
42. Brieger K, Schiavone S, Miller FJ Jr and Krause KH: Reactive oxygen species: from health to disease. Swiss Medical Weekly 2012; 142:w13659. doi: 10.4414/smw.2012.13659.142, p. w13659
43. Popa-Wagner A, Mitran S, Sivanesan S, Chang E and Buga AM: ROS and brain diseases: the good, the bad, and the ugly. Oxidative Medicine and Cellular Longevity 2013; 963520:2013. http://doi.org/10.1155/2013/963520.
44. Zhao Y and Zhao B: Oxidative stress and the pathogenesis of Alzheimer's disease. Oxidative Medicine and Cellular Longevity 2013; Article ID 316523, 10 pages, 2013. doi:10.1155/2013/316523
45. Pavelescu L: On reactive oxygen species measurement in living systems. Journal of Medicine and Life 2008; 8 (Special Issue):38-42.
46. Satyanarayana U, Kumar AN, Naidu JN and Viswa Prasad DK: Antioxidant supplementation for health - a boon or a bane? Journal of Dr. NTR University of Health Sciences 2014; 3: 221-230.
47. Rahman K: Studies on free radicals, antioxidants, and co-factors. Clinical Interventions in Aging 2007; 2(2):219–236.
48. Nordberg J and Arnér ES: Reactive oxygen species, antioxidants, and the mammalian thioredoxin system. Free Radical Biology and Medicine 2001; 31:1287-1312.
49. Gorrini C, Harris IS and Mak TW. Modulation of oxidative stress as an anticancer strategy. Nature Reviews Drug Discovery 2013; 12:931-947.
50. Zeng W, Xiao J, Zheng G, Xing F, Tipoe GL, Wang X, He C, Chen ZY, Liu Y: Antioxidant treatment enhances human mesenchymal stem cell anti-stress ability and therapeutic efficacy in an acute liver failure model. Scientific Reports 2015; 5: 11100. doi: 10.1038/srep11100.
51. Hsiang CY, Lo HY, Huang HC, Li CC, Wu SL and Ho TY: Ginger extract and zingerone ameliorated trinitrobenzene sulphonic acid-induced colitis in mice via modulation of nuclear factor-κB activity and interleukin-1β signalling pathway. Food Chemistry 2013; 136:170-177.
52. Singh S, Lata S and Tiwari KN: Protective role of Phyllanthus fraternus against cyclophosphamide induce nephrotoxicity in mice. Journal of Scientific Research 2014; 58:75-85.
53. Shin HS, Han JM, Kim HG, Choi MK, Son CG, Yoo HR, Jo HK and Seol IC: Anti-atherosclerosis and hyperlipidemia effects of herbal mixture, Artemisia iwayomogi Kitamura and Curcuma longa Linne, in apolipoprotein E-deficient mice. Journal of Ethnopharmacology 2014; 153:142-150.
54. Sankar SR, Manivasagam T, Krishnamurti A and Ramanathan M. The neuroprotective effect of Withania somnifera root extract in MPTP-intoxicated mice: an analysis of behavioral and biochemical variables. Cellular and Molecular Biology Letters 2007; 12: 473-481
55. Tripathy S. Stem cells: Hope and hype. Science Horizon 2015; 8:22-27.
56. He T, Peterson TE, Holmuhamedov EL, Terzic A, Caplice NM, Oberley LW and Katusic ZS: Human endothelial progenitor cells tolerate oxidative stress due to intrinsically high expression of manganese superoxide dismutase. Arteriosclerosis, Thrombosis, and Vascular Biology 2004; 24:2021-2027.
57. Krishnan A and Forman SJ: Hematopoietic Stem Cell Transplantation for AIDS related malignancies. Current opinion in oncology 2010; 22:456-460.
58. Bajada S, Mazakova I, Ashton BA, Richardson JB and Ashammakhi N: Stem cells in regenerative medicine. in Ashammakhi, Reis R and Chiellini F, editors. Topics in Tissue Engineering (2008); Vol. 4: Chapter 13, pp 1-28.
59. Sheng CC, Zhou Li and Hao J: Current Stem Cell Delivery Methods for Myocardial Repair. BioMed Research International 2013; (2013): 547902, 15 pages. doi:10.1155/2013/547902
60. Yim EK, Pang SW and Leong KW: Synthetic nanostructures inducing differentiation of human mesenchymal stem cells into neuronal lineage. Experimental Cell Research 2007; 313:1820-1829.
61. Ma DK, Bonaguidi MA, Ming GL and Song H: Adult neural stem cells in the mammalian central nervous system. Cell Research 2009; 19:672-682.
62. Tripathy S and Mohanty PK: Mesenchymal stem cells: a novel approach in regenerative medicine. World Journal of Pharmaceutical Research 2016; 2:410-433.
63. Kaseem M: Stem cells potential therapy for age-related diseases. Annual New York Academy of Sciences 2006; 1067:436-442.
64. Aleynik A, Gernavage KM, Mourad YS, Sherman LS, Liu K, Gubenko YA and Rameshwar P: Stem cell delivery of therapies for brain disorders. Clinical and Translational Medicine 2014; 3:24.
    

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    Tripathy S and Mohanty PK: Reactive oxygen species (ROS) are boon or bane. Int J Pharm Sci Res 2017; 8(1): 1-16.doi: 10.13040/IJPSR.0975-8232.8(1).1-16.

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